Active stylus with multiple sensors for receiving signals from a touch sensor

ABSTRACT

A stylus includes a first sensor configured to receive a first receive signal from a touch sensor of a device, and a second sensor configured to receive a second receive signal from the touch sensor of the device. The stylus includes an amplifier coupled to the first and second sensors and configured to produce a third signal by amplifying the difference between the first receive signal and the second receive signal. The stylus includes a controller configured to decode information encoded in the first receive signal and the second receive signal by processing the third signal.

TECHNICAL FIELD OF THE INVENTION

The present invention generally relates to touch sensors.

BACKGROUND

In an example scenario, a touch sensor detects the presence and positionof an object (e.g., a user's finger or a stylus) within atouch-sensitive area of touch sensor array overlaid on a display screen,for example. In a touch-sensitive-display application, a touch sensorarray allows a user to interact directly with what is displayed on thescreen, rather than indirectly with a mouse or touch pad. A touch sensormay be attached to or provided as part of a desktop computer, laptopcomputer, tablet computer, personal digital assistant (PDA), smartphone,satellite navigation device, portable media player, portable gameconsole, kiosk computer, point-of-sale device, or other appropriatedevice. A control panel on a household or other appliance may include atouch sensor.

There are a number of different types of touch sensors, such as (forexample) resistive touch sensors, surface acoustic wave touch sensors,and capacitive touch sensors. In one example, when an object physicallytouches a touch screen within a touch-sensitive area of a touch sensorof the touch screen (e.g., by physically touching a cover layeroverlaying a touch sensor array of the touch sensor) or comes within adetection distance of the touch sensor (e.g., by hovering above thecover layer overlaying the touch sensor array of the touch sensor), achange in capacitance may occur within the touch screen at a position ofthe touch sensor of the touch screen that corresponds to the position ofthe object within the touch sensitive area of the touch sensor. A touchsensor controller may process the change in capacitance to determine theposition of the change of capacitance within the touch sensor (e.g.,within a touch sensor array of the touch sensor).

BRIEF DESCRIPTION OF THE DRAWINGS

To provide a more complete understanding of the present disclosure andthe features and advantages thereof, reference is made to the followingdescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 illustrates an example touch sensor array with an example touchsensor controller according to an embodiment of the present disclosure;

FIG. 2 illustrates an example active stylus according to an embodimentof the present disclosure;

FIG. 3 illustrates example components of an active stylus according toan embodiment of the present disclosure;

FIG. 4 illustrates an example stylus input to a device according to anembodiment of the present disclosure;

FIGS. 5A-5B illustrate a portion of an example active stylus inproximity to a touch sensor of a device according to an embodiment ofthe present disclosure;

FIG. 6 illustrates in plan view an example arrangement of electrodes ofa touch sensor according to an embodiment of the present disclosure;

FIG. 7 illustrates example types of drive methods according to anembodiment of the present disclosure;

FIG. 8 illustrates an example method for receiving and processingsignals from a touch sensor using an active stylus according to anembodiment of the present disclosure; and

FIG. 9 illustrates an example device that uses the touch sensor of FIG.1 according to an embodiment of the present disclosure.

DESCRIPTION OF EXAMPLE EMBODIMENTS

When a stylus is used in conjunction with a device incorporating acapacitive touch sensor, the stylus typically receives signals from thetouch sensor in order to enable communication between the stylus and thetouch sensor. For example, the stylus may receive a synchronizationsignal from the touch sensor. However, the user's interactions with thedevice while holding the stylus (such as touching the edges of thedevice or placing a palm on the touch sensor) may cause the stylus topick up interfering signals. For example, because a user may be holdingthe outer body of the stylus, the user may inject signals into the localground of the stylus, such as signals generated by the touch sensor.

The present disclosure provides an apparatus and method to receive andprocess signals from the touch sensor even in scenarios where the usercouples signals into the stylus ground. For example, in one embodiment,the stylus includes two receive electrodes to receive signals from thetouch sensor, each having a different degree of capacitive coupling tothe touch sensor. The stylus also includes a differential amplifierwhich takes the received signal from both receive electrodes as an inputand produces an output signal that amplifies the difference between thetwo received signals.

In certain embodiments, the use of a differential amplifier connected totwo receiver electrodes may provide certain advantages as compared touse of an amplifier connected to a single receive electrode referencedagainst the local ground of active stylus. In a design where the localground of the stylus is used as a negative reference for the amplifier,a signal injected into the local ground of the stylus may reduce orinvert the amplifier's output signal because the injected signal wouldessentially be subtracted from the single receive electrode signal. Bycontrast, using the differential amplifier, the local stylus ground isnot used as an input. Therefore, the output of the differentialamplifier should be largely unaffected by signals injected into localground of active stylus by a user holding the stylus. Furthermore,because the differential amplifier amplifies the difference between thesignals from the two receiver electrodes, any noise or interferencecommon to both electrodes should be substantially reduced or cancelled.

In one embodiment, a stylus includes a first sensor disposed proximate afirst end of the stylus. The first sensor is adapted to receive a firstreceive signal via a first capacitive coupling with a touch sensor of adevice. The first end of the stylus is at a tip-end of the stylus. Thestylus also includes a second sensor disposed proximate the first end ofthe stylus. The second sensor is adapted to receive a second receivesignal via a second capacitive coupling with the touch sensor of thedevice. A proximity of the first sensor to the first end of the stylusis greater than a proximity of the second sensor to the first end of thestylus. A widest portion of the first sensor has a greater width than atleast a portion of the second sensor.

FIG. 1 illustrates an example touch sensor array with an example touchsensor controller according to an embodiment of the present disclosure.Touch sensor array 100 and touch sensor controller 102 detect thepresence and position of a touch or the proximity of an object within atouch-sensitive area of touch sensor array 100. Reference to a touchsensor array may encompass both touch sensor array 100 and its touchsensor controller. Similarly, reference to a touch sensor controller mayencompass both touch sensor controller 102 and its touch sensor array.Touch sensor array 100 includes one or more touch-sensitive areas. Inone embodiment, touch sensor array 100 includes an array of electrodesdisposed on one or more substrates, which may be made of a dielectricmaterial. Reference to a touch sensor array may encompass both theelectrodes of touch sensor array 100 and the substrate(s) on which theyare disposed. Alternatively, reference to a touch sensor array mayencompass the electrodes of touch sensor array 100, but not thesubstrate(s) on which they are disposed.

In one embodiment, an electrode is an area of conductive materialforming a shape, such as, for example, a disc, square, rectangle, thinline, other shape, or a combination of these shapes. One or more cuts inone or more layers of conductive material may (at least in part) createthe shape of an electrode, and the area of the shape may (at least inpart) be bounded by those cuts. In one embodiment, the conductivematerial of an electrode occupies approximately 100% of the area of itsshape. For example, an electrode may be made of indium tin oxide (ITO)and the ITO of the electrode may occupy approximately 100% of the areaof its shape (sometimes referred to as 100% fill). In one embodiment,the conductive material of an electrode occupies less than 100% of thearea of its shape. For example, an electrode may be made of fine linesof metal or other conductive material (FLM), such as, for example,copper, silver, or a copper- or silver-based material, and the finelines of conductive material may occupy approximately 5% of the area ofits shape in a hatched, mesh, or other pattern. Reference to FLMencompasses such material. Although this disclosure describes orillustrates particular electrodes made of particular conductive materialforming particular shapes with particular fill percentages havingparticular patterns, this disclosure contemplates electrodes made ofother conductive materials forming other shapes with other fillpercentages having other patterns.

The shapes of the electrodes (or other elements) of a touch sensor array100 constitute, in whole or in part, one or more macro-features of touchsensor array 100. One or more characteristics of the implementation ofthose shapes (such as, for example, the conductive materials, fills, orpatterns within the shapes) constitute in whole or in part one or moremicro-features of touch sensor array 100. One or more macro-features ofa touch sensor array 100 may determine one or more characteristics ofits functionality, and one or more micro-features of touch sensor array100 may determine one or more optical features of touch sensor array100, such as transmittance, refraction, or reflection.

Although this disclosure describes a number of example electrodes, thepresent disclosure is not limited to these example electrodes and otherelectrodes may be implemented. Additionally, although this disclosuredescribes a number of example embodiments that include particularconfigurations of particular electrodes forming particular nodes, thepresent disclosure is not limited to these example embodiments and otherconfigurations may be implemented. In one embodiment, a number ofelectrodes are disposed on the same or different surfaces of the samesubstrate. Additionally or alternatively, different electrodes may bedisposed on different substrates. Although this disclosure describes anumber of example embodiments that include particular electrodesarranged in specific, example patterns, the present disclosure is notlimited to these example patterns and other electrode patterns may beimplemented.

A mechanical stack contains the substrate (or multiple substrates) andthe conductive material forming the electrodes of touch sensor array100. For example, the mechanical stack may include a first layer ofoptically clear adhesive (OCA) beneath a cover panel. The cover panelmay be clear and made of a resilient material for repeated touching,such as, for example, glass, polycarbonate, or poly(methyl methacrylate)(PMMA). This disclosure contemplates the cover panel being made of anymaterial. The first layer of OCA may be disposed between the cover paneland the substrate with the conductive material forming the electrodes.The mechanical stack may also include a second layer of OCA and adielectric layer (which may be made of PET or another material, similarto the substrate with the conductive material forming the electrodes).As an alternative, a thin coating of a dielectric material may beapplied instead of the second layer of OCA and the dielectric layer. Thesecond layer of OCA may be disposed between the substrate with theconductive material making up the electrodes and the dielectric layer,and the dielectric layer may be disposed between the second layer of OCAand an air gap to a display of a device including touch sensor array 100and touch sensor controller 102. For example, the cover panel may have athickness of approximately 1 millimeter (mm); the first layer of OCA mayhave a thickness of approximately 0.05 mm; the substrate with theconductive material forming the electrodes may have a thickness ofapproximately 0.05 mm; the second layer of OCA may have a thickness ofapproximately 0.05 mm; and the dielectric layer may have a thickness ofapproximately 0.05 mm.

Although this disclosure describes a particular mechanical stack with aparticular number of particular layers made of particular materials andhaving particular thicknesses, this disclosure contemplates othermechanical stacks with any number of layers made of any materials andhaving any thicknesses. For example, in one embodiment, a layer ofadhesive or dielectric may replace the dielectric layer, second layer ofOCA, and air gap described above, with there being no air gap in thedisplay.

One or more portions of the substrate of touch sensor array 100 may bemade of polyethylene terephthalate (PET) or another material. Thisdisclosure contemplates any substrate with portions made of anymaterial(s). In one embodiment, one or more electrodes in touch sensorarray 100 are made of ITO in whole or in part. Additionally oralternatively, one or more electrodes in touch sensor array 100 are madeof fine lines of metal or other conductive material. For example, one ormore portions of the conductive material may be copper or copper-basedand have a thickness of approximately 5 microns (μm) or less and a widthof approximately 10 μm or less. As another example, one or more portionsof the conductive material may be silver or silver-based and similarlyhave a thickness of approximately 5 μm or less and a width ofapproximately 10 μm or less. This disclosure contemplates any electrodesmade of any materials.

In one embodiment, touch sensor array 100 implements a capacitive formof touch sensing. In a mutual-capacitance implementation, touch sensorarray 100 may include an array of drive and sense electrodes forming anarray of capacitive nodes. A drive electrode and a sense electrode mayform a capacitive node. The drive and sense electrodes forming thecapacitive node are positioned near each other but do not makeelectrical contact with each other. Instead, in response to a signalbeing applied to the drive electrodes, for example, the drive and senseelectrodes capacitively couple to each other across a space betweenthem. A pulsed or alternating voltage applied to the drive electrode (bytouch sensor controller 102) induces a charge on the sense electrode,and the amount of charge induced is susceptible to external influence(such as a touch or the proximity of an object). When an object touchesor comes within proximity of the capacitive node, a change incapacitance may occur at the capacitive node and touch sensor controller102 measures the change in capacitance. By measuring changes incapacitance throughout the array, touch sensor controller 102 determinesthe position of the touch or proximity within touch-sensitive areas oftouch sensor array 100.

In a self-capacitance implementation, touch sensor array 100 may includean array of electrodes of a single type that may each form a capacitivenode. When an object touches or comes within proximity of the capacitivenode, a change in self-capacitance may occur at the capacitive node andtouch sensor controller 102 measures the change in capacitance, forexample, as a change in the amount of charge implemented to raise thevoltage at the capacitive node by a pre-determined amount. As with amutual-capacitance implementation, by measuring changes in capacitancethroughout the array, touch sensor controller 102 determines theposition of the touch or proximity within touch-sensitive areas of touchsensor array 100. This disclosure contemplates any form of capacitivetouch sensing.

In one embodiment, one or more drive electrodes together form a driveline running horizontally or vertically or in other orientations.Similarly, in one embodiment, one or more sense electrodes together forma sense line running horizontally or vertically or in otherorientations. As one particular example, drive lines run substantiallyperpendicular to the sense lines. Reference to a drive line mayencompass one or more drive electrodes making up the drive line, andvice versa. Reference to a sense line may encompass one or more senseelectrodes making up the sense line, and vice versa.

In one embodiment, touch sensor array 100 includes drive and senseelectrodes disposed in a pattern on one side of a single substrate. Insuch a configuration, a pair of drive and sense electrodes capacitivelycoupled to each other across a space between them form a capacitivenode. As an example self-capacitance implementation, electrodes of asingle type are disposed in a pattern on a single substrate. In additionor as an alternative to having drive and sense electrodes disposed in apattern on one side of a single substrate, touch sensor array 100 mayhave drive electrodes disposed in a pattern on one side of a substrateand sense electrodes disposed in a pattern on another side of thesubstrate. Moreover, touch sensor array 100 may have drive electrodesdisposed in a pattern on one side of one substrate and sense electrodesdisposed in a pattern on one side of another substrate. In suchconfigurations, an intersection of a drive electrode and a senseelectrode forms a capacitive node. Such an intersection may be aposition where the drive electrode and the sense electrode “cross” orcome nearest each other in their respective planes. The drive and senseelectrodes do not make electrical contact with each other—instead theyare capacitively coupled to each other across a dielectric at theintersection. Although this disclosure describes particularconfigurations of particular electrodes forming particular nodes, thisdisclosure contemplates other configurations of electrodes formingnodes. Moreover, this disclosure contemplates other electrodes disposedon any number of substrates in any patterns.

As described above, a change in capacitance at a capacitive node oftouch sensor array 100 may indicate a touch or proximity input at theposition of the capacitive node. Touch sensor controller 102 detects andprocesses the change in capacitance to determine the presence andposition of the touch or proximity input. In one embodiment, touchsensor controller 102 then communicates information about the touch orproximity input to one or more other components (such as one or morecentral processing units (CPUs)) of a device that includes touch sensorarray 100 and touch sensor controller 102, which may respond to thetouch or proximity input by initiating a function of the device (or anapplication running on the device). Although this disclosure describes aparticular touch sensor controller having particular functionality withrespect to a particular device and a particular touch sensor, thisdisclosure contemplates any other touch sensor controllers having anyfunctionality with respect to any device and any touch sensor.

In one embodiment, touch sensor controller 102 is implemented as one ormore integrated circuits (ICs), such as, for example, general-purposemicroprocessors, microcontrollers, programmable logic devices or arrays,application-specific ICs (ASICs). Touch sensor controller 102 comprisesany combination of analog circuitry, digital logic, and digitalnon-volatile memory. In one embodiment, touch sensor controller 102 isdisposed on a flexible printed circuit (FPC) bonded to the substrate oftouch sensor array 100, as described below. The FPC may be active orpassive. In one embodiment, multiple touch sensor controllers 102 aredisposed on the FPC.

In an example implementation, touch sensor controller 102 includes aprocessor unit, a drive unit, a sense unit, and a storage unit. In suchan implementation, the drive unit supplies drive signals to the driveelectrodes of touch sensor array 100, and the sense unit senses chargeat the capacitive nodes of touch sensor array 100 and providesmeasurement signals to the processor unit representing capacitances atthe capacitive nodes. The processor unit controls the supply of drivesignals to the drive electrodes by the drive unit and processmeasurement signals from the sense unit to detect and process thepresence and position of a touch or proximity input withintouch-sensitive areas of touch sensor array 100. The processor unit mayalso track changes in the position of a touch or proximity input withintouch-sensitive areas of touch sensor array 100. The storage unit storesprogramming for execution by the processor unit, including programmingfor controlling the drive unit to supply drive signals to the driveelectrodes, programming for processing measurement signals from thesense unit, and other programming. Although this disclosure describes aparticular touch sensor controller having a particular implementationwith particular components, this disclosure contemplates a touch sensorcontroller having other implementations with other components.

Tracks 104 of conductive material disposed on the substrate of touchsensor array 100 couple the drive or sense electrodes of touch sensorarray 100 to connection pads 106, also disposed on the substrate oftouch sensor array 100. As described below, connection pads 106facilitate coupling of tracks 104 to touch sensor controller 102. Tracks104 may extend into or around (e.g., at the edges of) touch-sensitiveareas of touch sensor array 100. In one embodiment, particular tracks104 provide drive connections for coupling touch sensor controller 102to drive electrodes of touch sensor array 100, through which the driveunit of touch sensor controller 102 supplies drive signals to the driveelectrodes, and other tracks 104 provide sense connections for couplingtouch sensor controller 102 to sense electrodes of touch sensor array100, through which the sense unit of touch sensor controller 102 sensescharge at the capacitive nodes of touch sensor array 100.

Tracks 104 may be made of fine lines of metal or other conductivematerial. For example, the conductive material of tracks 104 may becopper or copper-based and have a width of approximately 100 μm or less.As another example, the conductive material of tracks 104 may be silveror silver-based and have a width of approximately 100 μm or less. In oneembodiment, tracks 104 are made of ITO in whole or in part in additionor as an alternative to the fine lines of metal or other conductivematerial. Although this disclosure describes particular tracks made ofparticular materials with particular widths, this disclosurecontemplates tracks made of other materials and/or other widths. Inaddition to tracks 104, touch sensor array 100 may include one or moreground lines terminating at a ground connector (which may be aconnection pad 106) at an edge of the substrate of touch sensor array100 (similar to tracks 104).

Connection pads 106 may be located along one or more edges of thesubstrate, outside touch-sensitive areas of touch sensor array 100. Asdescribed above, touch sensor controller 102 may be on an FPC.Connection pads 106 may be made of the same material as tracks 104 andmay be bonded to the FPC using an anisotropic conductive film (ACF). Inone embodiment, connection 108 includes conductive lines on the FPCcoupling touch sensor controller 102 to connection pads 106, in turncoupling touch sensor controller 102 to tracks 104 and to the drive orsense electrodes of touch sensor array 100. In another embodiment,connection pads 106 are connected to an electro-mechanical connector(such as a zero insertion force wire-to-board connector); in thisembodiment, connection 108 may not include an FPC, if desired. Thisdisclosure contemplates any connection 108 between touch sensorcontroller 102 and touch sensor array 100.

FIG. 2 illustrates an example exterior of an example active stylus 200.In an embodiment, active stylus 200 is powered (e.g., by an internal orexternal power source) and is capable of providing touch or proximityinputs to a touch sensor (e.g., touch sensor 100 illustrated in FIG. 1).Exemplary active stylus 200 includes one or more components, such asbuttons 230 or sliders 232 and 234 integrated with an outer body 222.These external components provide for interaction between active stylus200 and a user or between a device and a user. As an example and not byway of limitation, interactions include communication between activestylus 200 and a device, enabling or altering functionality of activestylus 200 or a device, or providing feedback to or accepting input fromone or more users. The device can be any suitable device, such as, forexample and without limitation, a desktop computer, laptop computer,tablet computer, personal digital assistant (PDA), smartphone, satellitenavigation device, portable media player, portable game console, kioskcomputer, or point-of-sale device. Although this disclosure providesspecific examples of particular components configured to provideparticular interactions, this disclosure contemplates any suitablecomponent configured to provide any suitable interaction. Active stylus200 can have any suitable dimensions with outer body 222 made of anysuitable material or combination of materials, such as, for example andwithout limitation, plastic or metal. In an embodiment, exteriorcomponents (e.g., 230 or 232) of active stylus 20 interact with internalcomponents or programming of active stylus 200 and initiate one or moreinteractions with one or more devices or other active styluses 200.

As described above, in an embodiment, actuating one or more particularcomponents initiates an interaction between active stylus 200 and a useror between the device and the user. Components of exemplary activestylus 200 include one or more buttons 230 or one or more sliders 232and 234. As an example and not by way of limitation, buttons 230 orsliders 232 and 234 can be mechanical or capacitive and can function asa roller, trackball, or wheel. As another example, one or more sliders232 or 234 can function as a vertical slider 234 aligned along alongitudinal axis of active stylus 200, while one or more wheel sliders232 can be aligned around the circumference of active stylus 200. In anembodiment, capacitive sliders 232 and 234 and buttons 230 areimplemented using one or more touch-sensitive areas. Touch-sensitiveareas can have any suitable shape, dimensions, location, or be made fromany suitable material. As an example and not by way of limitation,sliders 232 and 234 or buttons 230 are implemented using areas offlexible mesh formed using lines of conductive material. As anotherexample, sliders 232 and 234 or buttons 230 are implemented using a FPC.

Exemplary active stylus 200 has one or more components configured toprovide feedback to or accepting feedback from a user, such as, forexample and without limitation, tactile, visual, or audio feedback. Inan embodiment, active stylus 200 includes one or more ridges or grooves224 on its outer body 222. Ridges or grooves 224 can have any suitabledimensions, have any suitable spacing between ridges or grooves, or belocated at any suitable area on outer body 222 of active stylus 200. Asan example and not by way of limitation, ridges 224 enhance a user'sgrip on outer body 222 of active stylus 200 and provide tactile feedbackto or accept tactile input from a user. In an embodiment, active stylus200 includes one or more audio components 238 capable of transmittingand receiving audio signals. As an example and not by way of limitation,audio component 238 contains a microphone capable of recording ortransmitting one or more users' voices. As another example, audiocomponent 238 provides an auditory indication of a power status ofactive stylus 200. In an embodiment, active stylus 200 includes one ormore visual feedback components 236, such as a light-emitting diode(LED) indicator or electrophoretic ink (E-Ink). As an example and not byway of limitation, visual feedback component 236 indicates a powerstatus of active stylus 200 to the user.

In the depicted embodiment, one or more modified surface areas 240 formone or more components on outer body 222 of active stylus 200. In thisexample, properties of modified surface areas 240 are different thanproperties of the remaining surface of outer body 222. As an example andnot by way of limitation, modified surface area 240 can be modified tohave a different texture, temperature, or electromagnetic characteristicrelative to the surface properties of the remainder of outer body 222.As another example, modified surface area 240 is capable of dynamicallyaltering its properties, for example, by using haptic interfaces orrendering techniques. A user may interact with modified surface area 240to provide any suitable functionally. For example and not by way oflimitation, dragging a finger across modified surface area 240 caninitiate an interaction, such as data transfer, between active stylus200 and a device.

One or more components of active stylus 200 are configured tocommunicate data between active stylus 200 and the device. For example,active stylus 200 includes one or more tips 226 or nibs. Tip 226includes one or more sensors configured to communicate data betweenactive stylus 200 and one or more devices or other active styluses. Inan embodiment, tip 226 houses multiple sensors. For example, tip 226 caninclude two electrodes for receiving signals from a touch sensor, andone electrode for transmitting signals to a touch sensor. Examplesensors of tip 226 are described in more detail in connection with FIG.5. In an embodiment, tip 26 provides or communicates pressureinformation (e.g., the amount of pressure being exerted by active stylus200 through tip 226) between active stylus 200 and one or more devicesor other active styluses. Tip 226 may be made of any suitable material,such as a conductive material, and have any suitable dimensions, suchas, for example, a diameter of 1 mm or less at its terminal end.

Exemplary active stylus 200 includes one or more ports 228 located atsuitable locations on outer body 222 of active stylus 200. In anembodiment, port 228 is configured to transfer signals or informationbetween active stylus 200 and one or more devices or power sources via,for example, wired coupling. Port 228 can transfer signals orinformation by any suitable technology, such as, for example, byuniversal serial bus (USB) or Ethernet connections. Although thisdisclosure describes and illustrates a particular configuration ofparticular components with particular locations, dimensions, compositionand functionality, this disclosure contemplates any suitableconfiguration of suitable components with any suitable locations,dimensions, composition, and functionality with respect to active stylus200.

FIG. 3 illustrates example components of an active stylus 200 accordingto an embodiment of the present disclosure. Active stylus 200 includesone or more components, such as controller 302, sensors 304, memory 306,power source 308, and differential amplifier 316. In one embodiment, oneor more components are configured to provide for interaction betweenactive stylus 200 and a user or between a device and a user. Forexample, interactions include communication between active stylus 200and a device, enabling or altering functionality of active stylus 200 ora device, or providing feedback to or accepting input from one or moreusers. As another example, active stylus 200 may communicate via anyapplicable short distance, low energy data transmission or modulationlink, such as, for example, via a radio frequency (RF) communicationlink. In that implementation case, active stylus 200 includes a RFdevice for transmitting data over the RF link.

In one embodiment, differential amplifier 316 is coupled to twoelectrodes housed in stylus tip 310. Each of the two electrodes isadapted to receive signals from a touch sensor via a capacitive couplingbetween the touch sensor and the electrode. As one example, theelectrodes may receive a synchronization signal from the touch sensor,described in more detail in connection with FIG. 4. The differentialamplifier includes one or more digital or analog circuit elements thattakes the signals received at the two electrodes as inputs and producesan output signal that amplifies the difference between the two inputsignals. For example, differential amplifier 316 may use an op-amptaking the signal from the first electrode as a positive reference andthe signal from the second electrode as a negative reference. The outputsignal is then supplied to controller 302 for processing. In anembodiment, the differential amplifier also filters the output signalusing, for example, a bandpass filter. The filtering may help to rejectany noise which is not cancelled by the differential amplifier. In analternative embodiment, any necessary filtering is performed bycontroller 302.

In certain embodiments, the use of differential amplifier 316 connectedto two receiver electrodes may provide certain advantages as compared touse of an amplifier connected to a single receiver electrode referencedagainst the local ground of active stylus 200. Because a user may beholding the outer body of active stylus 200, the user may inject signalsinto the local ground of active stylus 200, such as signals generated bya device including a touch sensor. This is especially likely when theuser is simultaneously touching active stylus 200 and the device, asdescribed in more detail in FIG. 4. In a design where the local groundof active stylus 200 is used as a negative reference for the amplifier,the injected signal may reduce or invert the amplifier's output signalbecause the injected signal would essentially be subtracted from thesingle receiver electrode signal. By contrast, using differentialamplifier 316, the local stylus ground is not used as an input.Therefore, the output of differential amplifier should be largelyunaffected by signals injected into local ground of active stylus 200 bya user holding the stylus. Furthermore, because differential amplifier316 amplifies the difference between the signals from the two receiverelectrodes, any noise or interference common to both electrodes shouldbe substantially reduced or cancelled.

In certain embodiments, it may be desirable to optimize thecharacteristics of the two receiver electrodes to obtain certaincapacitive coupling relationships. As one example, it may be desirableto have the first receiver electrode (which is used as the positivereference for differential amplifier 316) have a larger signal magnitudethan the second receiver electrode (which is used as the negativereference for differential amplifier 316). If the two were equal inmagnitude, the signals would cancel entirely when applied todifferential amplifier 316. On the other hand, the larger the differencebetween the magnitude of the two signals, the larger will be themagnitude of the resulting output signal from differential amplifier316. In the case of a signal from the touch sensor, to accomplish thisresult, the capacitive coupling between the first receiver electrode andthe touch sensor should have a greater capacitance than the capacitivecoupling between the second receiver electrode. This and othercapacitive coupling relationships of the two receiver electrodes aredescribed in more detail in connection with FIG. 5.

In one embodiment, controller 302 is implemented as a microcontroller oranother type of processor for controlling the operation of active stylus200. As a particular example, controller 302 is implemented as one ormore ICs—such as, for example, general-purpose microprocessors,microcontrollers, PLDs, PLAs, or ASICs. In an example implementation,controller 302 includes a processor unit, a drive unit, a sense unit,and a storage unit. The drive unit supplies signals to electrodes of tip310 through center shaft 312. The drive unit may also supply signals tocontrol or drive sensors 304 or one or more external components ofactive stylus 200. In one embodiment, the drive unit of active stylus200 is configured to continuously (or at other time intervals or inresponse to other events) transmit a signal that may be detected byelectrodes of touch sensor array 100. For example, the drive unit ofactive stylus 200 may include a voltage pump, an oscillator, or aswitch, such that the voltage pump may generate a high voltage signal,the oscillator may generate a waveform such as a square wave or a sinewave, or the switch may toggle the potential of tip 310 between zerovoltage and a maximum voltage. The drive unit of active stylus 200 maytransmit a signal, such as a square wave or sine wave, that may besensed by the electrodes.

The sense unit obtains signals received by sensors housed in tip 310from differential amplifier 316 via center shaft 312 and providesmeasurement signals to the processor unit representing input from adevice. The sense unit may also sense signals generated by sensors 304or one or more external components and provide measurement signals tothe processor unit representing input from a user. The processor unitcontrols the supply of signals to the electrodes of tip 310 andprocesses measurement signals from the sense unit to detect and processinput from the device. The processor unit also decodes informationencoded in signals generated by a touch sensor. For example, theprocessor unit processes a header generated by a touch sensor in orderto synchronize communications between the stylus and the touch sensor,as described in more detail in connection with FIG. 4.

The processor unit may also process measurement signals from sensors 304or one or more external components. The storage unit stores programmingfor execution by the processor unit, including programming forcontrolling the drive unit to supply signals to the electrodes of tip310, programming for processing measurement signals from the sense unitcorresponding to input from the device, programming for processingmeasurement signals from sensors 304 or external components to initiatea pre-determined function or gesture to be performed by active stylus200 or the device, and other programming. For example, programmingexecuted by controller 302 may electronically filter signals receivedfrom the sense unit. Although this disclosure describes a particularcontroller 302 having a particular implementation with particularcomponents, this disclosure contemplates any controller having anyimplementation with any components.

In one embodiment, active stylus 200 includes one or more sensors 304,such as touch sensors, gyroscopes, accelerometers, contact sensors, orany other type of sensors that detect or measure data about theenvironment in which active stylus 200 Operates, Sensors 304 may detectand measure one or more characteristic of active stylus 200, such asacceleration or movement, orientation, contact, pressure on outer body314, force on tip 310, vibration, or any other characteristic of activestylus 200. For example, sensors 304 may be implemented mechanically,electronically, or capacitively. As described above, data detected ormeasured by sensors 304 communicated to controller 302 may initiate apre-determined function or gesture to be performed by active stylus 200or the device. In one embodiment, data detected or received by sensors304 may be stored in memory 306. Memory 306 is any form of memory forstoring data in active stylus 200. Controller 302 may access data storedin memory 306. For example, memory 306 may store programming forexecution by the processor unit of controller 302. As another example,data measured by sensors 304 may be processed by controller 302 andstored in memory 306.

Power source 308 is any type of stored-energy source, includingelectrical or chemical-energy sources, for powering the operation ofactive stylus 200. In one embodiment, power source 308 is charged withenergy from a user or device. For example, power source 308 may be arechargeable battery that is charged by motion induced on active stylus200. In other particular embodiments, power source 308 of active stylus200 provides power to or receives power from the device or otherexternal power source. For example, power may be inductively transferredbetween power source 308 and a power source of the device or otherexternal power source, such as a wireless power transmitter.Additionally or alternatively, power source 308 may be powered by awired connection through an applicable port coupled to a power source.

FIG. 4 illustrates an example stylus input to a device according to anembodiment of the present disclosure. Device 400 may have a display anda touch sensor array 100 with a touch-sensitive area 402. The display ofdevice 400 is any type of display, such as a liquid crystal display(LCD), a LED display, a LED-backlight LCD display, an active-matrixorganic LED (AMOLED) display, or other display, and may be visiblethough a cover panel and substrate (and the drive and sense electrodesof touch sensor array 100 disposed on it) of device 400. Although thisdisclosure describes a particular device display and particular displaytypes, this disclosure contemplates any device display and any displaytypes.

Device 400 electronics provide the functionality of device 400. Forexample, device 400 electronics may include circuitry or otherelectronics for wireless communication to or from device 400, executeprogramming on device 400, generating graphical or other user interfaces(UIs) for device 400 display to display to a user, managing power todevice 400 from a battery or other power source, taking still pictures,recording video, other functionality, or any combination of these.Although this disclosure describes particular device electronicsproviding particular functionality of a particular device, thisdisclosure contemplates any device electronics providing anyfunctionality of any device.

Touch sensor controller 102 of device 400 may operate in one or moremodes. In one embodiment, with respect to stylus interaction, touchsensor controller 102 may operate in at least the following two modes:“stylus not detected” and “stylus detected.” In the “stylus notdetected” mode, touch sensor controller 102 may interleave or otherwisemix self-capacitance, mutual capacitance, and active stylus 200 “notdetected” mode measurements to detect touch or proximity inputs,including, for example, the presence of active stylus 200 during thesame measurement cycle. Each of these types of measurements may be usedto detect certain types of inputs performed on or above touch-sensitivearea 402. For example, touch sensor controller 102 may useself-capacitance measurements to detect certain touch or proximityinputs. In one embodiment, touch sensor controller 102 may useself-capacitance measurements to detect single-finger touches or largearea palm touches. As another example, touch sensor controller 102 mayuse mutual capacitance measurements to detect certain touch or proximityinputs. In one embodiment, touch sensor controller 102 may use mutualcapacitance measurements to detect multiple small touches or multi-touchinput. As described below, touch sensor controller 102 may make the“stylus not detected” measurements using a modified self-capacitancemeasurement configured to provide position data of active stylus 200above touch-sensitive area 402; however, the present disclosurecontemplates touch sensor controller 102 making the “stylus notdetected” measurements using any technique.

Although particular measurement types are described as being used todetect particular types of touch or proximity inputs, the presentdisclosure contemplates using any type of measurement to detect any typeof touch or proximity input. For example, the present disclosurecontemplates using any of the above-described measurement types todetect any type of touch or proximity input. As used herein, the terms“touch” and “proximity” may be used interchangeably to refer to bothphysical touches (e.g., of touch sensor array 100 or a cover layeroverlaying touch sensor array 100) by an object (e.g., a finger, palm,stylus, or other object) and presence of an object (e.g., a finger,palm, stylus, or other object) within a detectable range of touch sensorarray 100 where the object does not necessarily physically contact touchsensor array 100 (or a cover layer overlaying touch sensor array 100).For example, a touch or proximity input may refer to an input where anobject is in physical contact with the cover panel of a device.Additionally or alternatively, a touch or proximity input may refer todetecting an object within a particular distance (e.g., hovering) overthe cover panel (e.g., hovering).

In one embodiment, when touch sensor controller of device 400 hasdetected active stylus 200 within touch-sensitive area 402, touch sensorcontroller 102 may enter (or remain in, if appropriate) the “stylusdetected” mode. In the “stylus detected” mode, touch sensor controller102 may discontinue some measurements (e.g., self-capacitance and mutualcapacitance, if appropriate) and perform measurements specific tocommunicating with active stylus 200. In one embodiment, the “stylusdetected” mode may use a communication scheme between active stylus 200and device 400 that includes a synchronization phase and a listen phase.For example, in the synchronization phase active stylus 200 may besynchronized to device 400 prior to the communication of other databetween active stylus 200 and device 400. In one embodiment, thissynchronization is performed through a synchronization (“sync”) signaltransmitted by the electrodes of touch-sensitive area 402 to activestylus 200. In one embodiment, the synchronization signal comprises apre-determined bit sequence, e.g., a pulse wave. For example, thesynchronization signal may be a square wave, sine wave, or any voltagewaveform. Although particular techniques for interleaving or otherwisemixing different proximity detection modes are described, the presentdisclosure contemplates interleaving or otherwise mixing proximitydetection modes according to any desired implementation.

In one embodiment, in the listen phase, active stylus 200 detects thesynchronization signal and active stylus 200 responds with acommunication signal (e.g., a series of pulses) onto which data isencoded. For example, touch sensor controller 102 may sample integratorsconnected to electrodes of touch-sensitive area 402 at pre-determinedtime intervals that correspond to the frequency of the synchronizationsignal. In one embodiment, the synchronization signal may initiate,provide for, or terminate the communication signal between active stylus200 and one or more devices 400 or one or more users.

As a particular example of communication between the touch sensor andstylus 200, a header is a signal transmitted from touch controller 102to stylus 200 via one or more electrodes 204. In one embodiment, aheader includes one or more signal pulses upon which information isencoded. Stylus 200 listens for these pulses and responds once it hasreceived a complete set of pulses (e.g., a complete “header”). In oneembodiment, the response from stylus 200 includes one or more signalpulses upon which information is encoded for transmission to touchcontroller 102 via one or more electrodes 204.

When the housing of device 400 is held by the user, the electrodes ofdevice 400 are capacitively coupled to the hand that is holding device400 through the self-capacitance of the electrodes of device 400 and thebody of the user. An object, such as a finger or stylus, in proximity tothe electrodes defining touch-sensitive area 402 may initiate a transferof an amount of charge between the object and the electrodes of device400. Given the user is holding the outer body of active stylus 200,which is coupled to a local ground of active stylus 200, the user cancouple a signal (e.g., a synchronization signal) transmitted by device400 to the local ground of active stylus 200. For example, if the userplaces a large area touch (e.g., through a palm touch) located above theelectrodes of touch sensor array 100 that receive the applied signal,the applied signal may be coupled into the local ground of active stylus200 through the user holding device 400.

FIGS. 5A-5B illustrate a portion of an example active stylus 200 inproximity to a touch sensor 100 of a device according to an embodimentof the present disclosure. Only a portion of the tip-end of activestylus 200 is depicted, including a portion of stylus barrel 508,transmit electrode 506, first receive electrode 504, and second receiveelectrode 502. In an embodiment, electrodes 502, 504, and 506 would behoused within a tip assembly, which is not depicted in FIGS. 5A-5B. Inthe example of FIGS. 5A-5B, electrodes 502, 504, and 506 each have agenerally conical shape. In particular, each electrode is a truncatedcone (i.e., a section of a cone having a particular, height, top radius,and bottom radius). Although electrodes 502, 504, and 506 are depictedas solid, in some embodiments, the electrodes may not be entirelyarea-filling. For example, each electrode may be formed of a shapedspring, whose outermost extent generally corresponds to the electrodeshapes depicted in FIGS. 5A-5B. In an alternative embodiment to the onedepicted in FIGS. 5A-5B, transmit electrode 506 and first receiveelectrode 504 may be replaced by a single electrode adapted to bothtransmit and receive signals.

In the preferred embodiment, first receive electrode 504 has a bottomradius 522 of 3 mm, a top radius 524 of between 3 and 5 mm (preferably4.5 mm), and a height 520 of between 4 and 6 mm (preferably 5.8 min). Inthe preferred embodiment, second receive electrode 502 has a bottomradius 528 of between 3 and 5 mm (preferably 3.38 mm), a top radius 530of between 5 and 7 mm (preferably 6.08 mm), and a height 526 of between6 and 10 mm (preferably 6.9 mm). In the preferred embodiment, the firstreceive electrode 504 and second receive electrode 502 are separated byan electrode gap 532 of between 0.1 and 1 mm, such as 0.5 mm.

In the example of FIG. 5A, capacitances 512, 514, 516, and 518 representcapacitive couplings between portions of active stylus 200 and touchsensor 100. Capacitance 512 represents a capacitive coupling betweenfirst receive electrode 504 and a first signal present on electrodes ina first portion 509 of touch sensor 100. The first signal may be aheader signal or other synchronization signal. Capacitance 516represents a capacitive coupling between first receive electrode 504 anda second signal present on electrodes in a second portion 510 of touchsensor 100. The second signal may be a ground reference of touch sensor100. Alternatively, the second signal may be an inverted version of thefirst signal (i.e., the second signal may have reversed polaritycompared to the first signal).

Capacitance 514 represents a capacitive coupling between second receiveelectrode 502 and the first signal present on electrodes in firstportion 509 of touch sensor 100. Capacitance 518 represents a capacitivecoupling between second receive electrode 502 and the second signalpresent on electrodes in second portion 510 of touch sensor 100.

In general, the strength of the depicted capacitive couplings (i.e., themagnitude of the capacitance) depends upon the area of the coupledportions and the distance between them. Increasing the surface area of areceive electrode will generally increase its capacitive coupling withtouch sensor 100. Likewise, a smaller distance between the receiveelectrode and the touch sensor will generally increase its capacitivecoupling with touch sensor 100. By selecting an appropriate size, shape,placement, and arrangement of the first receive electrode 504 and thesecond receive electrode 502, the relationships of between the depictedcapacitive couplings can be optimized to maximize the quality of thereceived signal as output from differential amplifier 316.

In the preferred embodiment, capacitive coupling 512 is greater thancapacitive coupling 514. In other words, first receiver 504 has agreater capacitive coupling to the first signal (such as a headersignal) than does second receiver 502. The greater the differencebetween these couplings, the larger the difference between the magnitudeof the header signal that will couple to each receiver. Increasing thisdifference improves the performance of differential amplifier 316because it amplifies the difference between the signals received at thetwo electrodes.

In the preferred embodiment, the sum of capacitive couplings 512 and 516is approximately equal to the sum of capacitive couplings 514 and 518.In other words, the total coupling of first receiver 504 to touch sensor100 is approximately equal to the total coupling of second receiver 502to touch sensor 100. Furthermore, in the preferred embodiment, firstreceiver 504 will have a coupling to the local stylus ground (notdepicted) that is approximately equal to the coupling between secondreceiver 502 and the local stylus ground. As described above, signalsmay be injected into the local stylus ground by a user of the stylus. Bymatching the coupling to local stylus ground, approximately the sameamount of injected signal should appear at both receive electrodes,allowing differential receiver 316 to substantially reduce or entirelycancel the injected signal, as well as other common noise that couplesto the local stylus ground.

In the example of FIG. 5A, active stylus 200 is oriented at an angle ofapproximately 90 degrees relative to the surface of touch sensor 100. Inthe preferred embodiment, the above-described relationships betweencapacitive couplings may be achieved not only at approximately 90degrees relative to the surface of touch sensor 100, but also over arange of angles up to and including approximately 45 degrees relative tothe surface of touch sensor 100. In the depicted embodiment, the shapesand sizes of the first receive electrode 504 and second receiveelectrode 502 have been selected such that the widest portion of firstreceive electrode 504 has a greater width than portions of secondreceive electrode 502. For example, the top radius 524 of first receiveelectrode 504 is greater than the bottom radius 528 of second receiveelectrode 502. Thus, at an angle of approximately 90 degrees, the topportion of first receive electrode 504 at least partially shields thebottom portion of second receive electrode 502 relative to the portionof touch sensor 100 directly below the stylus tip, effectively reducingthe area of second receive electrode 502 available to capacitivelycouple with touch sensor 100. However, as stylus 100 tilts away from 90degrees toward 45 degrees, the degree of shielding provided by the wideportion of first receive electrode 504 decreases.

In the example of FIG. 5B, active stylus 200 is oriented at an angle ofapproximately 45 degrees relative to the surface of touch sensor 100. Inthis orientation, the distance between first receive electrode 504 andtouch sensor 100 is much smaller than in FIG. 5A, which greatlyincreases capacitive coupling 512. In order to maintain the capacitivecoupling relationships described above, there would need to be acorresponding increase in capacitive coupling 514. In the depictedexample, this is achieved because as the stylus tilts away from 90degrees, more and more of the bottom, narrow portion of second receiveelectrode 502 is exposed and available to capacitively couple to touchsensor 100.

FIG. 6 illustrates in plan view an example electrode pattern 500 ofelectrodes 204 of touch sensor array 100, according to an embodiment ofthe present disclosure. Electrodes 204 a are oriented in a firstdirection and electrodes 204 b are oriented in a second directiondifferent from the first direction, such that touch-sensitive area 602of touch sensor array 100 is defined by the two-dimensional array ofelectrodes 204 a and electrodes 204 b. In the illustrated example, thefirst direction and the second direction are perpendicular to eachother. Electrodes 204 a and electrodes 204 b may be described based ontheir orientation in touch sensor array 100. For example, electrodesoriented along a horizontal direction (electrodes 204 a in theillustrated example) may be referred to as x-electrodes and electrodesoriented along a vertical direction (electrodes 204 b in the illustratedexample) may be referred to as y-electrodes.

Electrodes 204 a and electrodes 204 b overlap at points along theelectrodes. In a mutual capacitive mode of operation, capacitive nodesare formed at areas (e.g., area 26) where electrodes 204 overlap whenone of electrodes 204 a and 204 b operates as a drive electrode and theother of electrodes 204 a and 204 b operates as a sense electrode andwhen a drive signal is applied to the electrodes 204 operating as driveelectrodes.

In one embodiment, electrodes 204 a and electrodes 204 b are disposed onthe same side of a substrate. In such embodiments, to ensure thatelectrodes 204 a and electrodes 204 b are electrically isolated from oneanother, electrodes 204 a and electrodes 204 b are separated by adielectric or other material at points where electrodes 204 a andelectrodes 204 b overlap. In certain other embodiments, electrodes 204 aand electrodes 204 b are disposed on opposing sides of a substrate, thesubstrate being made of a dielectric or other material that electricallyisolates electrodes 204 a and electrodes 204 b from one another. Incertain other embodiments, electrodes 204 a and electrodes 204 b aredisposed on respective surfaces of different substrates, which arepositioned with respect to each other such that electrodes 204 a andelectrodes 204 b are electrically isolated from each other at pointswhere electrodes 204 a and electrodes 204 b overlap. For example, one ormore of the substrates may be positioned between electrodes 204 a(positioned on one of the substrates) and electrodes 204 b (positionedon the other of the substrates) or an additional substrate, such as adielectric substrate, or air gap is sandwiched between the twosubstrates on which electrodes 204 a and electrodes 204 b are formed.

Although this disclosure describes a touch sensor including electrodes204 having particular orientations, this disclosure contemplates anytouch sensor with electrodes having any orientations. Additionally, theparticular shapes and arrangement of electrodes 204 shown and describedwith respect to FIG. 6 are provided for example purposes only. Thepresent disclosure contemplates electrodes 204 having any shapes (orcombination of shapes) and any arrangement (or combination ofarrangement).

In one embodiment, electrodes 204 b operate as drive electrodes andelectrodes 204 a operate as sense electrodes. In other embodiments,electrodes 204 a operate as drive electrodes and electrodes 204 boperate as sense electrodes. In one embodiment, both electrodes 204 aand electrodes 204 b operate as sense electrodes. In one embodiment, aportion or all of electrodes 204 a are configurable to operate as senseelectrodes during some measurements and as drive electrodes during othermeasurements. Additionally or alternatively, in one embodiment, aportion or all of electrodes 204 b are configurable to operate as senseelectrodes during some measurements and as drive electrodes during othermeasurements. As an example, during a first mode of operation, a portionor all of electrodes 204 a and a portion or all of electrodes 204 boperate as sense electrodes and during a second mode of operation, aportion or all of electrodes 204 b operate as drive electrodes and aportion or all of electrodes 204 a operate as sense electrodes.

In one particular example implementation, in a stylus detection mode, aportion or all of both electrodes 204 a and electrodes 204 b operate asdrive electrodes during a first phase in which a drive signal is appliedto the electrodes and then operate as sense electrodes during a secondphase in which touch sensor array 100 awaits a response from a stylus(e.g., stylus 200) in proximity to touch sensor array 100 (if a stylusis in proximity).

As described above, in the “stylus not detected” mode, touch sensorcontroller may perform a modified self-capacitance measurement todetermine the position of a stylus (e.g., stylus 200) in proximity totouch-sensitive area 402 defined by electrodes 204 a and electrodes 204b. Touch sensor controller 102 may drive a set 106 a of one or moreelectrodes 204 of touch sensor array 100 to transmit the applied signal,e.g., synchronization signal, to search for a stylus (e.g., stylus 200)in proximity to touch sensor array 100. The position of active stylus200 may be determined by controller 102 transmitting a synchronizationsignal via electrodes 204 and “listening” for a signal transmitted bystylus 200 in response to stylus 200 receiving the synchronizationsignal. In one embodiment, touch sensor controller 102 may apply thesynchronization signal to one or more electrodes 204. For example, thesignal applied to electrodes 204 a may include a number of pulses thathave an amplitude that corresponds to a pre-determined peak voltage,such as a supply voltage. Although this disclosure describes techniquesfor locating and synchronizing with a stylus (e.g., stylus 200) usingparticular voltages, this disclosure contemplates any techniques forlocating and synchronizing with a stylus using any voltages.

In one embodiment, controller 102 toggles between performing ameasurement for detecting of the presence of a stylus using electrodes204 a and performing a measurement for detecting the presence of astylus using electrodes 204 b. Although this technique for detecting thepresence of a stylus is described, the present disclosure contemplatesapplying drive signals (for detecting the presence of a stylus) in anymanner and using any portion of electrodes 204.

Stylus 200, when in proximity to touch sensor array 100, may transmit asignal in response to the synchronization signal transmitted by touchsensor array 100. The response signal communicated by stylus 200 may bereceived by one or more electrodes 204 a and one or more electrodes 204b of touch sensor array 100. Touch sensor controller 102 may process thereceived signal to determine a position of stylus 200. For example,touch sensor controller 102 may determine that stylus 200 is located inproximity to touch sensor array 100 at the position based on identifyingone or more x-electrodes and y-electrodes receiving the largestamplitude signal from stylus 200. Although a particular technique fordetermining position is described, the present disclosure contemplatestouch sensor controller 102 determining the position of stylus 200according to any technique.

FIG. 7 illustrates example types of drive methods 700, according to anembodiment of the present disclosure. Drive methods 700 are used bycontroller 102, for example, to apply drive signals to a portion or allof electrodes 204. During each drive method 700, a particular voltage isapplied, or no voltage is applied, for a time period. Example drivemethods 700 a, 700 b, and 700 c are described below. Column 702 aidentifies the name of the drive method. Column 702 b identifies thefill type used to illustrate the associated drive method. For example, adotted fill is used to represent drive method 700 a, a striped fill isused to represent drive method 700 b, and a no fill is used to representdrive method 700 c. Column 702 c includes an illustration of an exampledrive signal 704 for the associated drive method 700.

Drive method 700 a represents an example drive method in whichcontroller 102 applies a drive signal 704 a having a first polarity toone or more electrodes 204. In an embodiment, controller 102 isconfigured to apply drive signal 704 a to electrodes 204 to search for astylus in proximity to touch sensor array 100.

Drive method 700 b represents an example drive method in whichcontroller 102 applies an unmodulated signal or a zero-volt signal 704 bto one or more electrodes 204. For simplicity, drive signal 704 b ofdrive method 700 b is referred to as zero-volt signal 704 b.

Drive method 700 c represents an example drive method in whichcontroller 102 applies a drive signal 704 c having a second polarity toone or more electrodes 204. The second polarity of drive signal 704 c isdifferent than the first polarity of drive signal 704 a. In oneembodiment, the second polarity of drive signal 704 c is the inverse ofthe first polarity of drive signal 704 a such that drive signal 704 c isan inverted drive signal 704 relative to drive signal 704 a. Forexample, drive signal 704 c includes a peak 706 c that is an inverse ofcorresponding peak 706 a of drive signal 704 a. In one embodiment, drivesignal 704 c and drive signal 704 a have the same waveform (e.g., havingthe same magnitudes and periods) but are polar opposites of one another.As a particular example, drive signal 704 c and drive signal 704 a areboth square waveforms having the same magnitudes and periods, but arepolar opposites of one another. For purposes of the present disclosure,drive signal 704 c may be referred to as inverted drive signal 704 c.

Embodiments of the present disclosure use some or all of these differentdrive methods 600 and corresponding drive signals 704 (drive signal 704a, zero-volt signal 704 b, and inverted drive signal 704 c to cause astylus (e.g., stylus 200) to send different types of signals to besensed by controller 102 on electrodes 204. For example, whileelectrodes 204 may typically be driven using drive method 700 a (drivesignal 704 a having the first polarity) or drive method 700 b (zero-voltsignal 704 b), it may be desirable to drive one or more electrodes 204according to drive method 700 c (using inverted drive signal 704 c).

Although particular types of drive signals are illustrated anddescribed, the present disclosure contemplates using any types of drivesignals. For example, although particular patterns are illustrated anddescribed, other patterns may be used. As a particular example, althoughsquare wave drive signals are shown, the present disclosure contemplatesusing sine wave drive signals. Additionally, the present disclosurecontemplates using drive signals having any phase(s), frequency(ies),amplitude(s), number of pulses, and other characteristics.

FIG. 8 illustrates an example method for receiving and processingsignals from a touch sensor using an active stylus 200, according to anembodiment of the present disclosure. In one embodiment, some or all ofthese steps are performed while a touch sensor controller 102 of adevice is in a stylus scan mode of operation of controller 102. Asdescribed above, the stylus scan mode may be interleaved or otherwisemixed with other modes of operation of controller 102.

At step 802, active stylus 200 receives a first receive signal from atouch sensor of a device via a capacitive coupling between the firstreceive electrode of the stylus and a signal generated by the touchsensor. For example, controller 102 may drive touch sensor electrodes204 using drive method 700 a with drive signal 704 a.

The drive signal 704 may be a header signal to cause stylus 200 totransmit a responsive signal. In one embodiment, the header signalincludes one or more signal pulses upon which information is encoded.

At step 804, active stylus 200 receives a second receive signal from atouch sensor of a device via a capacitive coupling between the secondreceive electrode of the stylus and the signal generated by the touchsensor. As discussed above, the signal generated by the touch sensor maybe a header signal. In an embodiment, the first receive electrode of thestylus has a greater degree of capacitive coupling to the header signalthan does the second receive electrode of the stylus. As a result, thefirst receive signal may have a greater magnitude than the secondreceive signal. Thus, both the first receive signal and the secondreceive signals should include the header signal (with varying magnitudebased on capacitive coupling) plus some noise. In an embodiment, steps802 and 804 may occur simultaneously or sequentially but very close intime.

At step 806, active stylus 200 produces a third signal by amplifying thedifference between the first receive signal and the second receivesignal. Differential amplifier 316 takes the signals received by thefirst and second receive electrodes of the stylus as its positive andnegative inputs, respectively. Any noise common to both the firstreceive signal and the second receive signal should be substantiallyreduced or eliminated. The header signal component should remain and beamplified, as both signals contain varying amounts of the header signalbecause of the differences in the capacitive coupling between the headersignal and the two receivers. The resulting third signal is provided tostylus controller 302.

At step 808, active stylus 200 decodes information encoded in the firstreceive signal and second receive signal by processing the third signal.As discussed above, the third signal provides the header signal withadditional noise reduced or removed. Stylus controller 302 uses thethird signal to retrieve the information encoded on the pulses of theheader signal.

At step 810, active stylus 200 determines whether it has received acomplete header based at least in part on the decoded information. Ifnot, the method returns to step 802 where the active stylus 200continues to receive signals from the touch sensor of the device. If so,the method proceeds to step 812.

At step 812, active stylus 200 transmits a response to the touch sensorof the device. In one embodiment, the response from stylus 200 includesone or more signal pulses upon which information is encoded fortransmission to touch controller 102 via one or more electrodes 204.

Although this disclosure describes and illustrates particular steps ofthe method of FIG. 8 as occurring in a particular order, this disclosurecontemplates steps of the method of FIG. 8 occurring in any order.Particular embodiments may repeat one or more steps of the method ofFIG. 8. Moreover, although this disclosure describes and illustrates anexample method for receiving and processing signals from a touch sensorusing an active stylus including the particular steps of the method ofFIG. 8, this disclosure contemplates any method for receiving andprocessing signals from a touch sensor using an active stylus includingany steps, which may include all, some, or none of the steps of themethod of FIG. 8. Moreover, although this disclosure describes andillustrates particular components performing particular steps of themethod of FIG. 8, this disclosure contemplates any combination of anycomponents performing any steps of the method of FIG. 8.

FIG. 9 illustrates an example device 900 that uses touch sensor array100 of FIG. 1, according to an embodiment of the present disclosure.Device 900 includes any personal digital assistant, cellular telephone,smartphone, tablet computer, and the like. In one embodiment, device 900includes other applications such as automatic teller machines (ATMs),home appliances, personal computers, and any other such device having atouch screen. For example, a certain embodiment of device 900 is asmartphone that includes a touch screen display 902 occupying asignificant portion of a surface of the device. In one embodiment, thelarge size of touch screen display 902 allows the touch screen display902 to present a wide variety of data, including a keyboard, a numerickeypad, program or application icons, and various other interfaces asdesired. In one embodiment, a user interacts with device 900 by touchingtouch screen display 902 with a stylus, a finger, or any otherappropriate object in order to interact with device 900 (e.g., select aprogram for execution or to type a letter on a keyboard displayed on thetouch screen display 902). In one embodiment, a user interacts withdevice 900 using multiple touches to perform various operations, such asto zoom in or zoom out when viewing a document or image. In someembodiments, such as home appliances, touch screen display 902 does notchange or changes only slightly during device operation, and recognizesonly single touches.

Herein, a computer-readable non-transitory storage medium or media mayinclude one or more semiconductor-based or other integrated circuits(ICs) (such, as for example, field-programmable gate arrays (FPGAs) orapplication-specific ICs (ASICs)), hard disk drives (HDDs), hybrid harddrives (HHDs), optical discs, optical disc drives (ODDs),magneto-optical discs, magneto-optical drives, floppy diskettes, floppydisk drives (FDDs), magnetic tapes, solid-state drives (SSDs),RAM-drives, SECURE DIGITAL cards or drives, any other computer-readablenon-transitory storage media, or any combination of two or more ofthese. A computer-readable non-transitory storage medium may bevolatile, non-volatile, or a combination of volatile and non-volatile.

Herein, “or” is inclusive and not exclusive, unless expressly indicatedotherwise or indicated otherwise by context. Therefore, herein, “A or B”means “A, B, or both,” unless expressly indicated otherwise or indicatedotherwise by context. Moreover, “and” is both joint and several, unlessexpressly indicated otherwise or indicated otherwise by context.Therefore, herein, “A and B” means “A and B, jointly or severally,”unless expressly indicated otherwise or indicated otherwise by context.

This disclosure encompasses a myriad of changes, substitutions,variations, alterations, and modifications to the example embodimentsherein that a person having ordinary skill in the art would comprehend.Similarly, the appended claims encompass all changes, substitutions,variations, alterations, and modifications to the example embodimentsherein that a person having ordinary skill in the art would comprehend.Moreover, reference in the appended claims to an apparatus or system ora component of an apparatus or system being adapted to, arranged to,capable of, configured to, enabled to, operable to, or operative toperform a particular function encompasses that apparatus, system,component, whether or not it or that particular function is activated,turned on, or unlocked, as long as that apparatus, system, or componentis so adapted, arranged, capable, configured, enabled, operable, oroperative.

1. A stylus comprising: a first sensor configured to receive a firstreceive signal from a touch sensor of a device; a second sensorconfigured to receive a second receive signal from the touch sensor ofthe device; and a controller configured to: decode information encodedin the first receive signal and the second receive signal; determinewhether a complete header is received based at least in part on thedecoded information; and responsive to determining that a completeheader is received, controls transmitting a response to the touch sensorof the device.
 2. The stylus of claim 1, further comprising an amplifiercoupled to the first and second sensors and configured to produce athird signal by amplifying the difference between the first receivesignal and the second receive signal.
 3. The stylus of claim 2, whereinthe amplifier is a differential amplifier configured to receive thefirst receive signal via one input and the second receive signal viaanother input.
 4. The stylus of claim 1, wherein, the first sensor isdisposed proximate a first end of the stylus and adapted to receive thefirst receive signal via a first capacitive coupling with the touchsensor of the device, the first end of the stylus being at a tip-end ofthe stylus, and the second sensor is disposed proximate the first end ofthe stylus and adapted to receive the second receive signal via a secondcapacitive coupling with the touch sensor of the device.
 5. The stylusof claim 4, wherein, the first sensor has a third capacitive couplingwith a local stylus ground, the second sensor has a fourth capacitivecoupling with the local stylus ground, and the controller is configuredto reduce common noise injected to the local stylus ground by a user ofthe stylus.
 6. The stylus of claim 5, wherein the common noiseoriginates from a sensor signal of the touch sensor of the device. 7.The stylus of claim 5, wherein a capacitance of the third capacitivecoupling between the first sensor and the local stylus ground isapproximately equal to a capacitance of the fourth capacitive couplingbetween the second sensor and the local stylus ground.
 8. The stylus ofclaim 4, wherein a proximity of the first sensor to the first end of thestylus is greater than a proximity of the second sensor to the first endof the stylus.
 9. The stylus of claim 4, wherein the first sensor has agenerally conical shape with a radius that generally decreases along alength of the stylus in a direction toward the first end of the stylus.10. The stylus of claim 1, wherein a widest portion of the first sensorhas a greater width than at least a portion of the second sensor. 11.The stylus of claim 1, wherein the shape of the first sensor is atruncated cone.
 12. The stylus of claim 1, wherein a largest width ofthe first sensor is larger than a smallest width of the second sensor.